Vincente Valtieri is the gang vampire. He's the most obvious vampire in the game and is quite kind to you. Since he's your first guy to award quests he always gives you helpful advice.
A Watery Grave
Ok this time you've got to kill a pirate on-board his ship. There's no bonus so just go at night when he's sleeping. Go to the Waterfront district of the Imperial city and there should be 2 ships, The floating Bloat and the pirate ship. Walk on-board the pirate ship and go into sneak mode and go into the small extremely obvious door to your left. The captain should be sleeping in his bed a few feet away. Stay in stealth mode and stab him in the back a few times once he's dead loot him quickly and get off the boat. Pirates will come to see what's going on and if they see you you'll have an unnecessary fight on your hands.
Accidents Happen
This quest is the first time you have a bonus. A man needs to be killed but it has to look like an accident. That rules out the usual stab 20 times in the face as well as bashing his face in with a mace. So what to do? When you're getting the quest Valtieri suggests you loosen the Minotaur head above the victims chair so we'll try that if we want the bonus.
Before you do this though make sure you have a few lockpicks. If you need you can buy em from Ongar a few buildings away from your victim. That is if you're in the Thieves' Guild of course. The best time to go into the house is 8 pm since it gives you plenty of time to get it done.
So go around behind his house and pick the lock to break into his basement. You're going to want to be in stealth mode from here on out. You can steal whatever you want down here since there is no one downstairs. Now pick the lock on the door up to the first floor, and remember BE IN STEALTH MODE. No sneak along in the shadows. If you look to your right you'll see your target sitting contently talking with his huge orc body guard, good thing we don't have to fight him. So carefully sneaking around the doorway and head upstairs. You can steal whatever you want from up here too since no one is looking. In one of the two bedrooms there will be a portion of wall that you can open and enter a small passage way. Move to then end and make sure it's between 8 and 11 (That's when he's in the chair) and undo the knotting and listen as it falls and kills him.
Now you'd think the orc would be after you, but since he thinks it's an accident he just stands gasping at his master. DO NOT KILL THE ORC, if you do then you will not get the bonus for making the quest look like an accident. Steal anything you still want and sneak out the way you came. Head back to the Dark Brotherhood to turn in. Valtieri will give you your money as well as Sufferthorn (a fairly nice dagger) if you made it look like and didn't kill the orc as told not to.
Scheduled for Execution
You know you've been thinking about this since the first minutes of the game. Killing that damn insulting Dark Elf in the cell across from you. When that secret passage opened up you thought to yourself "someday when I'm powerful I will come back through here and kill him." Well now you get to do it and you get paid to boot.
Vincent gives you the key that lets you get back into the sewers you escaped from so very long ago. Head back in and you'll find it's full of guards. Really they probably only needed one or two guards stationed at the entrance, but whatever.
So sneak through the sanctuary and come back to your old cell. Wait for a moment and listen to the Dark Elves' crazy dreams of escape and glory. Wait for the guard to leave, open your door and shoot a couple arrows through the bars at him.
Head up the stairs and walk out of the prison, head back to Vincent for your reward. Still can't believe you got paid to do that can you?
The Assassinated Man
This quest is a bit on the odd side. A man has hired assassins to fake his death. Yeah that's a good idea. But we get a bonus so off we go.
When you're assigned the quest Vincent gives you a poison dagger and the antidote (you see the plan yet?) Meet the "victim" (Motierre) and talk to him, he'll ask you to wait for the real assassin (gangster) to show up. Quickly stab Motierre with the poison dagger. The other assassin will try to attack you (Why? you just did his job for him) so run out of the house fast.
Come back in town and sleep/wait for about a day. Head to the church basement and give him the antidote. He'll mention that this is his family's tomb. Then he'll mention that his family will see this as desecration and LOOK A ZOMBIE. So you'll have to fight 3 or 4 zombies down here (what do ya know you got to kill something after all!) and escort him to the inn (he apperently thinks that a public place would be a good place to hide) and head back to Vincent for your reward.